{"id":48284,"date":"2019-11-10T00:04:11","date_gmt":"2019-11-09T23:04:11","guid":{"rendered":"https:\/\/www.thermal-engineering.org\/o-que-e-trabalho-em-termodinamica-definicao\/"},"modified":"2020-01-28T14:21:40","modified_gmt":"2020-01-28T13:21:40","slug":"o-que-e-trabalho-em-termodinamica-definicao","status":"publish","type":"post","link":"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-trabalho-em-termodinamica-definicao\/","title":{"rendered":"O que \u00e9 trabalho em termodin\u00e2mica &#8211; defini\u00e7\u00e3o"},"content":{"rendered":"<div class=\"su-quote su-quote-style-default\">\n<div class=\"su-quote-inner su-clearfix\">Na termodin\u00e2mica, o trabalho realizado por um sistema \u00e9 a energia transferida pelo sistema para os arredores.\u00a0O trabalho \u00e9 uma forma de energia, mas \u00e9 energia em tr\u00e2nsito.\u00a0Engenharia T\u00e9rmica<\/div>\n<\/div>\n<div class=\"su-divider su-divider-style-dotted\"><\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spacer\"><\/div>\n<h2>Trabalho em Termodin\u00e2mica<\/h2>\n<p>Na termodin\u00e2mica, o\u00a0<strong>trabalho<\/strong>\u00a0realizado por um sistema \u00e9 a energia transferida pelo sistema para os arredores.\u00a0Energia cin\u00e9tica, energia potencial e energia interna s\u00e3o formas de energia que s\u00e3o propriedades de um sistema.\u00a0<strong>O trabalho \u00e9 uma forma de energia<\/strong>\u00a0, mas \u00e9\u00a0<strong>energia em tr\u00e2nsito<\/strong>\u00a0.\u00a0Um sistema n\u00e3o cont\u00e9m trabalho, trabalho \u00e9 um processo realizado por ou em um sistema.\u00a0Em geral, o trabalho \u00e9 definido para sistemas mec\u00e2nicos como a a\u00e7\u00e3o de uma for\u00e7a sobre um objeto a dist\u00e2ncia.<\/p>\n<p><strong><em>W = F.\u00a0d<\/em><\/strong><\/p>\n<p>Onde:<\/p>\n<p>W = trabalho (J)<\/p>\n<p>F = for\u00e7a (N)<\/p>\n<p>d = deslocamento (m)<\/p>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spacer\"><\/div>\n<h2>Trabalho p\u0394V<\/h2>\n<figure id=\"attachment_16883\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-16883\"><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/pdV-Work-Thermodynamics.png\"><img loading=\"lazy\" class=\"size-medium wp-image-16883 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/pdV-Work-Thermodynamics-300x242.png\" alt=\"Trabalho pdV - Termodin\u00e2mica\" width=\"300\" height=\"242\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/pdV-Work-Thermodynamics-300x242.png\" \/><\/a><figcaption id=\"caption-attachment-16883\" class=\"wp-caption-text\">p\u0394V O trabalho \u00e9 igual \u00e0 \u00e1rea sob a curva do processo plotada no diagrama press\u00e3o-volume.<\/figcaption><\/figure>\n<p>O trabalho press\u00e3o-volume (ou\u00a0<strong><em>p\u0394V<\/em><\/strong><strong>\u00a0Work<\/strong>\u00a0) ocorre quando o volume\u00a0<em>V<\/em>\u00a0de um sistema \u00e9 alterado.\u00a0O\u00a0<strong>trabalho\u00a0<\/strong><strong><em>p\u0394V<\/em><\/strong>\u00a0\u00e9 igual \u00e0 \u00e1rea sob a curva do processo plotada no diagrama press\u00e3o-volume.\u00a0\u00c9 conhecido tamb\u00e9m como o\u00a0<strong>trabalho de fronteira<\/strong>\u00a0.\u00a0<strong>O trabalho de limite<\/strong>\u00a0\u00a0ocorre porque a massa da subst\u00e2ncia contida no limite do sistema faz com que uma for\u00e7a, a press\u00e3o vezes a \u00e1rea da superf\u00edcie, atue na superf\u00edcie do limite e fa\u00e7a com que ela se mova.\u00a0<strong>O trabalho de limite<\/strong>\u00a0\u00a0(ou\u00a0\u00a0<em><strong>p\u0394V<\/strong><\/em><strong>\u00a0Work<\/strong>\u00a0) ocorre quando o\u00a0\u00a0<strong>volume\u00a0<\/strong><em><strong>V<\/strong><\/em><strong>\u00a0de um sistema \u00e9 alterado<\/strong>\u00a0.\u00a0\u00c9 usado para calcular o trabalho de deslocamento do pist\u00e3o em um\u00a0\u00a0<strong>sistema fechado<\/strong>.\u00a0\u00c9 o que acontece quando o\u00a0\u00a0<a href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-o-steam-propriedades-do-steam-definicao\/\"><strong>vapor<\/strong><\/a>\u00a0ou o g\u00e1s contido em um dispositivo de cilindro e pist\u00e3o se expande contra o pist\u00e3o e for\u00e7a o pist\u00e3o a se mover.<\/p>\n<p><strong>Exemplo:<\/strong><\/p>\n<p>Considere-se um pist\u00e3o de atrito que \u00e9 usado para proporcionar uma press\u00e3o constante de\u00a0<strong>500 kPa<\/strong>\u00a0num cilindro contendo vapor (\u00a0<a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-steam-what-is-steam\/superheated-steam\/\">vapor sobreaquecido<\/a>\u00a0) de um volume de\u00a0<strong>2 m\u00a0<\/strong><strong><sup>3<\/sup><\/strong>\u00a0\u00a0a\u00a0<strong>500 K<\/strong>\u00a0.<\/p>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights  lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<p><span>Calcule a temperatura final, se\u00a0<\/span><strong><span>3000 kJ<\/span><\/strong><span>\u00a0de\u00a0<\/span><strong><span>calor<\/span><\/strong><span>\u00a0forem adicionados.<\/span><\/p>\n<figure id=\"attachment_16678\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-16678\"><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Enthalpy-example-min.png\"><img loading=\"lazy\" class=\"size-medium wp-image-16678 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Enthalpy-example-min-224x300.png\" alt=\"Entalpia - Exemplo - Um pist\u00e3o sem atrito\" width=\"224\" height=\"300\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Enthalpy-example-min-224x300.png\" \/><\/a><figcaption id=\"caption-attachment-16678\" class=\"wp-caption-text\"><span>Calcule a temperatura final, se 3000 kJ de calor forem adicionados.<\/span><\/figcaption><\/figure>\n<p><strong><span>Solu\u00e7\u00e3o:<\/span><\/strong><\/p>\n<p><span>Usando\u00a0<\/span><a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/steam-tables\/\"><span>tabelas de vapor<\/span><\/a><span>\u00a0, sabemos que a\u00a0<\/span><strong><span>entalpia espec\u00edfica<\/span><\/strong><span>\u00a0desse vapor (500 kPa; 500 K) \u00e9 de cerca de\u00a0<\/span><strong><span>2912 kJ \/ kg<\/span><\/strong><span>\u00a0.\u00a0Como nessa condi\u00e7\u00e3o o vapor possui densidade de 2,2 kg \/ m\u00a0<\/span><sup><span>3<\/span><\/sup><span>\u00a0, sabemos que h\u00e1 cerca de\u00a0<\/span><strong><span>4,4 kg de vapor<\/span><\/strong><span>\u00a0no pist\u00e3o na entalpia de 2912 kJ \/ kg x 4,4 kg =\u00a0<\/span><strong><span>12812 kJ<\/span><\/strong><span>\u00a0.<\/span><\/p>\n<p><span>Quando usamos simplesmente\u00a0<\/span><strong><span>Q = H\u00a0<\/span><\/strong><strong><sub><span>2<\/span><\/sub><\/strong><strong><span>\u00a0&#8211; H\u00a0<\/span><\/strong><strong><sub><span>1<\/span><\/sub><\/strong><span>\u00a0, a entalpia resultante do vapor ser\u00e1:<\/span><\/p>\n<p><span>H\u00a0<\/span><sub><span>2<\/span><\/sub><span>\u00a0= H\u00a0<\/span><sub><span>1<\/span><\/sub><span>\u00a0+ Q =\u00a0<\/span><strong><span>15812 kJ<\/span><\/strong><\/p>\n<p><span>Nas\u00a0<\/span><strong><span>tabelas de vapor<\/span><\/strong><span>\u00a0, esse vapor superaquecido (15812 \/ 4,4 = 3593 kJ \/ kg) ter\u00e1 uma temperatura de\u00a0<\/span><strong><span>828 K (555 \u00b0 C)<\/span><\/strong><span>\u00a0.\u00a0Uma vez que nesta entalpia do vapor tem a densidade de 1,31 kg \/ m\u00a0<\/span><sup><span>3<\/span><\/sup><span>\u00a0, \u00e9 \u00f3bvio que se expandiu em cerca de 2,2 \/ 1,31 = 1,67 (+ 67%).\u00a0Portanto, o volume resultante \u00e9 de 2 m\u00a0<\/span><sup><span>3<\/span><\/sup><span>\u00a0x 1,67 = 3,34 m\u00a0<\/span><sup><span>3<\/span><\/sup><span>\u00a0e \u2206V = 3,34 m\u00a0<\/span><sup><span>3<\/span><\/sup><span>\u00a0&#8211; 2 m\u00a0<\/span><sup><span>3<\/span><\/sup><span>\u00a0= 1,34 m\u00a0<\/span><sup><span>3<\/span><\/sup><span>\u00a0.<\/span><\/p>\n<p><span>A\u00a0parte\u00a0<\/span><strong><span>p\u2206V<\/span><\/strong><span>\u00a0da entalpia, ou seja, o trabalho realizado \u00e9:<\/span><\/p>\n<p><strong><span>W = p\u2206V = 500 000 Pa x 1,34 m\u00a0<\/span><\/strong><strong><sup><span>3<\/span><\/sup><\/strong><strong><span>\u00a0= 670 kJ<\/span><\/strong><\/p>\n<p><span>\u2014\u2014\u2014\u2013<\/span><\/p>\n<p><span>Durante a\u00a0<\/span><strong><span>mudan\u00e7a de volume<\/span><\/strong><span>\u00a0, a\u00a0<\/span><strong><span>press\u00e3o<\/span><\/strong><span>\u00a0e a\u00a0<\/span><strong><span>temperatura<\/span><\/strong><span>\u00a0tamb\u00e9m podem mudar.\u00a0Para calcular esses processos, precisar\u00edamos saber como a press\u00e3o varia com o volume do processo real pelo qual o sistema muda\u00a0<\/span><strong><span>do estado i para o estado f<\/span><\/strong><span>\u00a0.\u00a0A\u00a0<\/span><strong><span>primeira lei da termodin\u00e2mica<\/span><\/strong><span>\u00a0e o trabalho podem ser expressos como:<\/span><\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Work-in-Thermodynamics-general-formula.png\"><img loading=\"lazy\" class=\"size-full wp-image-16887 aligncenter lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Work-in-Thermodynamics-general-formula.png\" alt=\"Trabalho em Termodin\u00e2mica - f\u00f3rmula geral\" width=\"145\" height=\"148\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Work-in-Thermodynamics-general-formula.png\" \/><\/a><\/p>\n<figure id=\"attachment_16884\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-16884\"><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Work-in-Thermodynamics-path-dependency.png\"><img loading=\"lazy\" class=\"wp-image-16884 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Work-in-Thermodynamics-path-dependency.png\" alt=\"Trabalho em Termodin\u00e2mica - depend\u00eancia de caminho\" width=\"256\" height=\"628\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Work-in-Thermodynamics-path-dependency.png\" \/><\/a><figcaption id=\"caption-attachment-16884\" class=\"wp-caption-text\"><span>O trabalho realizado pelo sistema depende n\u00e3o apenas dos estados inicial e final, mas tamb\u00e9m dos estados intermedi\u00e1rios &#8211; ou seja, no caminho.<\/span><\/figcaption><\/figure>\n<p><span>Quando um sistema termodin\u00e2mico muda de um\u00a0<\/span><strong><span>estado inicial<\/span><\/strong><span>\u00a0para um\u00a0<\/span><strong><span>estado final<\/span><\/strong><span>\u00a0, ele passa por uma\u00a0<\/span><strong><span>s\u00e9rie de estados intermedi\u00e1rios<\/span><\/strong><span>\u00a0.\u00a0Chamamos essa s\u00e9rie de estados de\u00a0<\/span><strong><span>caminho<\/span><\/strong><span>\u00a0.\u00a0Sempre existem infinitas possibilidades para esses estados intermedi\u00e1rios.\u00a0Quando todos eles s\u00e3o estados de equil\u00edbrio, o caminho pode ser plotado em um\u00a0<\/span><strong><span>diagrama pV<\/span><\/strong><span>\u00a0.\u00a0Uma das conclus\u00f5es mais importantes \u00e9 que:<\/span><\/p>\n<p><em><span>O trabalho realizado pelo sistema depende n\u00e3o apenas dos estados inicial e final, mas tamb\u00e9m dos estados intermedi\u00e1rios &#8211; ou seja, no caminho.<\/span><\/em><\/p>\n<p><strong><span>Q e W s\u00e3o dependentes do caminho, enquanto \u0394E\u00a0<\/span><\/strong><strong><sub><span>int<\/span><\/sub><\/strong><strong><span>\u00a0\u00e9 independente do caminho.\u00a0<\/span><\/strong><span>Como pode ser visto na figura (diagrama pV), o trabalho \u00e9 vari\u00e1vel dependente do caminho.\u00a0A \u00e1rea azul representa o\u00a0<strong>trabalho\u00a0<\/strong><\/span><strong><em><span>p\u0394V<\/span><\/em><\/strong><span>\u00a0realizado por um sistema, que passa de um estado inicial i para um estado final f.\u00a0O trabalho W \u00e9 positivo porque o volume do sistema aumenta.\u00a0O segundo processo mostra que o trabalho \u00e9 maior e depende do caminho do processo.<\/span><\/p>\n<p><span>Al\u00e9m disso, podemos conduzir o sistema atrav\u00e9s de uma s\u00e9rie de estados formando um\u00a0<\/span><strong><span>circuito fechado<\/span><\/strong><span>\u00a0, como\u00a0<\/span><strong><span>i \u21d2 f \u21d2 i<\/span><\/strong><span>\u00a0.\u00a0Nesse caso, o\u00a0<\/span><strong><span>estado final \u00e9 o mesmo que o estado inicial<\/span><\/strong><span>\u00a0, mas o\u00a0<\/span><strong><span>trabalho total realizado<\/span><\/strong><span>\u00a0pelo sistema\u00a0<\/span><strong><span>n\u00e3o \u00e9 zero<\/span><\/strong><span>\u00a0.\u00a0Um valor positivo para o trabalho indica que o trabalho \u00e9 realizado pelo sistema em seus arredores.\u00a0Um valor negativo indica que o trabalho \u00e9 realizado no sistema por seus arredores.<\/span><\/p>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights  lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spacer\"><\/div>\n<h2><span>Exemplo: Trabalho Espec\u00edfico da Turbina<\/span><\/h2>\n<figure id=\"attachment_16026\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-16026\"><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Thermodynamic-Cycles-min.png\"><img loading=\"lazy\" class=\"size-medium wp-image-16026 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Thermodynamic-Cycles-min-300x277.png\" alt=\"termodin\u00e2mica de engenharia\" width=\"300\" height=\"277\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Thermodynamic-Cycles-min-300x277.png\" \/><\/a><figcaption id=\"caption-attachment-16026\" class=\"wp-caption-text\"><span>Ciclo de Rankine &#8211; Termodin\u00e2mica como ci\u00eancia de convers\u00e3o de energia<\/span><\/figcaption><\/figure>\n<p><span>Um\u00a0<\/span><strong><span>est\u00e1gio<\/span><\/strong><span>\u00a0de\u00a0<strong>alta press\u00e3o<\/strong>\u00a0da\u00a0<\/span><strong><span>turbina a vapor<\/span><\/strong><span>\u00a0opera em estado estacion\u00e1rio com condi\u00e7\u00f5es de entrada de \u00a0\u00a0<\/span><strong><span>6 MPa<\/span><\/strong><span>\u00a0,\u00a0<\/span><strong><span>t = 275,6 \u00b0 C<\/span><\/strong><span>\u00a0, x = 1 (ponto C).\u00a0Vapor folhas esta etapa de turbina a uma press\u00e3o de\u00a0<\/span><strong><span>1,15 MPa<\/span><\/strong><span>\u00a0,\u00a0<\/span><strong><span>186 \u00b0 C<\/span><\/strong><span>\u00a0e\u00a0<\/span><strong><span>x = 0,87<\/span><\/strong><span>\u00a0(ponto D).\u00a0Calcule a diferen\u00e7a de entalpia entre esses dois estados.\u00a0Determine a transfer\u00eancia de trabalho espec\u00edfica.<\/span><\/p>\n<p><span>A\u00a0<\/span><a title=\"O que \u00e9 entalpia\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/what-is-energy-physics\/what-is-enthalpy\/\"><span>entalpia<\/span><\/a><span>\u00a0para o estado C pode ser coletada diretamente das\u00a0<\/span><a title=\"Tabelas de Vapor - Propriedades Espec\u00edficas da \u00c1gua e Vapor\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/steam-tables\/\"><strong><span>tabelas de vapor<\/span><\/strong><\/a><span>\u00a0, enquanto a entalpia para o estado D deve ser calculada usando a\u00a0<\/span><a title=\"Qualidade de Vapor - Fra\u00e7\u00e3o de Secura\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-steam-what-is-steam\/vapor-quality-dryness-fraction\/\"><span>qualidade do vapor<\/span><\/a><span>\u00a0:<\/span><\/p>\n<p><strong><em><span>h\u00a0<\/span><\/em><\/strong><strong><em><sub><span>1, molhado<\/span><\/sub><\/em><\/strong><strong><em><span>\u00a0=<\/span><\/em><\/strong><strong><span>\u00a02785 kJ \/ kg<\/span><\/strong><\/p>\n<p><strong><em><span>h\u00a0<\/span><\/em><\/strong><strong><em><sub><span>2, molhado<\/span><\/sub><\/em><\/strong><strong><em><span>\u00a0= h\u00a0<\/span><\/em><\/strong><strong><em><sub><span>2, s<\/span><\/sub><\/em><\/strong><strong><em><span>\u00a0x + (1 &#8211; x) h\u00a0<\/span><\/em><\/strong><strong><em><sub><span>2, l<\/span><\/sub><\/em><\/strong><span>\u00a0\u00a0= 2782.\u00a00,87 + (1 &#8211; 0,87).\u00a0790 = 2420 + 103 =<\/span><strong><span>\u00a02523 kJ \/ kg<\/span><\/strong><\/p>\n<p><strong><span>\u0394h = 262 kJ \/ kg<\/span><\/strong><\/p>\n<p><span>Como no processo adiab\u00e1tico\u00a0<\/span><strong><span>dh = dw<\/span><\/strong><span>\u00a0,\u00a0<\/span><strong><span>\u0394h = 262 kJ \/ kg \u00e9<\/span><\/strong><span>\u00a0o\u00a0<\/span><strong><span>trabalho espec\u00edfico<\/span><\/strong><span>\u00a0da\u00a0<strong>turbina<\/strong>\u00a0.<\/span><\/p>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights  lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spacer\"><\/div>\n<h2><span>Primeira lei em termos de entalpia dH = dQ + Vdp<\/span><\/h2>\n<p><span>A\u00a0<\/span><a title=\"O que \u00e9 entalpia\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/what-is-energy-physics\/what-is-enthalpy\/\"><strong><span>entalpia<\/span><\/strong><\/a><span>\u00a0\u00e9 definida como sendo a soma da\u00a0<\/span><a href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-energia-interna-energia-termica-definicao\/\"><span>energia interna<\/span><\/a><span>\u00a0E mais o produto da\u00a0<\/span><a title=\"O que \u00e9 press\u00e3o - F\u00edsica\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/thermodynamic-properties\/what-is-pressure-physics\/\"><span>press\u00e3o P<\/span><\/a><span>\u00a0e\u00a0<\/span><a title=\"O que \u00e9 volume - F\u00edsica\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/thermodynamic-properties\/what-is-volume-physics\/\"><span>volume V<\/span><\/a><span>\u00a0.\u00a0Em muitas an\u00e1lises termodin\u00e2micas, a soma da energia interna U e o produto da press\u00e3o pe volume V aparece; portanto, \u00e9 conveniente atribuir \u00e0 combina\u00e7\u00e3o um nome,\u00a0<\/span><strong><span>entalpia<\/span><\/strong><span>\u00a0e um s\u00edmbolo distinto, H.<\/span><\/p>\n<p><em><strong><span>H = U + pV<\/span><\/strong><\/em><\/p>\n<p><span>Veja tamb\u00e9m:\u00a0<\/span><a title=\"O que \u00e9 entalpia\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/what-is-energy-physics\/what-is-enthalpy\/\"><span>Entalpia<\/span><\/a><\/p>\n<p><span>A\u00a0<\/span><strong><span>primeira lei da termodin\u00e2mica<\/span><\/strong><span>\u00a0em termos de\u00a0<\/span><strong><span>entalpia<\/span><\/strong><span>\u00a0mostra-nos por que os engenheiros usam a entalpia em ciclos termodin\u00e2micos (por exemplo,\u00a0<\/span><strong><span>ciclo de Brayton<\/span><\/strong><span>\u00a0ou\u00a0<\/span><strong><span>ciclo de Rankine<\/span><\/strong><span>\u00a0).<\/span><\/p>\n<p><span>A forma cl\u00e1ssica da lei \u00e9 a seguinte equa\u00e7\u00e3o:<\/span><\/p>\n<p><em><strong><span>dU = dQ &#8211; dW<\/span><\/strong><\/em><\/p>\n<p><span>Nesta equa\u00e7\u00e3o,\u00a0<\/span><strong><span>dW<\/span><\/strong><span>\u00a0\u00e9 igual a\u00a0<\/span><strong><span>dW = pdV<\/span><\/strong><span>\u00a0e \u00e9 conhecido como\u00a0<\/span><strong><span>trabalho de fronteira<\/span><\/strong><span>\u00a0.<\/span><\/p>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights  lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<div class=\"su-divider su-divider-style-dotted\"><\/div>\n<p><span>Como\u00a0<\/span><strong><em><span>H = U + pV<\/span><\/em><\/strong><span>\u00a0, portanto\u00a0<\/span><em><strong><span>dH = dU + pdV + Vdp<\/span><\/strong><\/em><span>\u00a0e substitu\u00edmos\u00a0<\/span><em><strong><span>dU = dH &#8211; pdV &#8211; Vdp<\/span><\/strong><\/em><span>\u00a0na forma cl\u00e1ssica da lei:<\/span><em><strong><span>dH &#8211; pdV &#8211; Vdp = dQ &#8211; pdV<\/span><\/strong><\/em><\/p>\n<p><span>Obtemos a lei em termos de entalpia:<\/span><\/p>\n<p><strong><em><span>dH = dQ + Vdp<\/span><\/em><\/strong><\/p>\n<p><span>ou<\/span><\/p>\n<p><strong><em><span>dH = TdS + Vdp<\/span><\/em><\/strong><\/p>\n<p><span>Nesta equa\u00e7\u00e3o, o termo\u00a0<\/span><em><strong><span>Vdp<\/span><\/strong><\/em><span>\u00a0\u00e9 um\u00a0<\/span><strong><span>trabalho de processo de fluxo.\u00a0<\/span><\/strong><span>Este trabalho, \u00a0\u00a0<\/span><em><strong><span>Vdp<\/span><\/strong><\/em><span>\u00a0, \u00e9 usado para\u00a0<\/span><strong><span>sistemas de fluxo aberto,<\/span><\/strong><span>\u00a0como uma\u00a0<\/span><strong><span>turbina<\/span><\/strong><span>\u00a0ou uma\u00a0<\/span><strong><span>bomba<\/span><\/strong><span>\u00a0na qual existe um\u00a0<\/span><strong><span>&#8220;dp&#8221;<\/span><\/strong><span>\u00a0, ou seja, mudan\u00e7a de press\u00e3o.\u00a0N\u00e3o h\u00e1 altera\u00e7\u00f5es no\u00a0<\/span><a title=\"Controle de volume - An\u00e1lise de volume de controle\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/control-volume-control-volume-analysis\/\"><span>volume de controle<\/span><\/a><span>\u00a0.\u00a0Como pode ser visto, essa forma de lei\u00a0<\/span><strong><span>simplifica a descri\u00e7\u00e3o da transfer\u00eancia de energia<\/span><\/strong><span>\u00a0.\u00a0<\/span><strong><span>A press\u00e3o constante<\/span><\/strong><span>\u00a0, a\u00a0<\/span><strong><span>mudan\u00e7a de entalpia<\/span><\/strong><span>\u00a0\u00e9 igual \u00e0\u00a0<\/span><strong><span>energia<\/span><\/strong><span>\u00a0transferida do ambiente atrav\u00e9s do aquecimento:<\/span><\/p>\n<p><strong><span>Processo isob\u00e1rico (Vdp = 0):<\/span><\/strong><\/p>\n<p><strong><span>dH = dQ \u00a0 \u00a0\u00a0\u00a0<\/span><span>\u2192<\/span><span>\u00a0\u00a0 \u00a0 \u00a0Q = H\u00a0<\/span><\/strong><strong><sub><span>2<\/span><\/sub><\/strong><strong><span>\u00a0&#8211; H\u00a0<\/span><\/strong><strong><sub><span>1<\/span><\/sub><\/strong><\/p>\n<p><strong><span>Na entropia constante<\/span><\/strong><span>\u00a0, ou seja, no processo isentr\u00f3pico, a\u00a0<\/span><strong><span>mudan\u00e7a de entalpia<\/span><\/strong><span>\u00a0\u00e9 igual ao\u00a0<\/span><strong><span>trabalho do processo de fluxo<\/span><\/strong><span>\u00a0realizado no ou pelo sistema:<\/span><\/p>\n<p><strong><span>Processo isentr\u00f3pico (dQ = 0):<\/span><\/strong><\/p>\n<p><strong><span>dH = Vdp\u00a0 \u00a0 \u00a0\u00a0<\/span><span>\u2192<\/span><span>\u00a0\u00a0 \u00a0 \u00a0W = H\u00a0<\/span><\/strong><strong><sub><span>2<\/span><\/sub><\/strong><strong><span>\u00a0&#8211; H\u00a0<\/span><\/strong><strong><sub><span>1<\/span><\/sub><\/strong><\/p>\n<p><span>\u00c9 \u00f3bvio que ser\u00e1 muito \u00fatil na an\u00e1lise de ambos os ciclos termodin\u00e2micos usados \u200b\u200bna engenharia de energia, ou seja, no ciclo de Brayton e no ciclo de Rankine.<\/span><\/p>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights  lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spacer\"><\/div>\n<h2><span>Exemplo: Primeira Lei da Termodin\u00e2mica e Ciclo de Brayton<\/span><\/h2>\n<p><span>Vamos assumir o\u00a0<\/span><strong><span>ciclo de Brayton ideal<\/span><\/strong><span>\u00a0que descreve o funcionamento de um\u00a0<strong>motor de calor com\u00a0<\/strong><\/span><strong><span>press\u00e3o constante<\/span><\/strong>\u00a0<span>.\u00a0<strong>Os modernos<\/strong>\u00a0motores de\u00a0<strong>turbina a g\u00e1s<\/strong>\u00a0e os motores a\u00a0<strong>jato de respira\u00e7\u00e3o<\/strong>\u00a0tamb\u00e9m seguem o ciclo de Brayton.\u00a0Esse ciclo consiste em quatro processos termodin\u00e2micos:<\/span><\/p>\n<ol>\n<li>\n<figure id=\"attachment_16843\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-16843\"><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/first-law-example-brayton-cycle.png\"><img loading=\"lazy\" class=\"size-medium wp-image-16843 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/first-law-example-brayton-cycle-300x244.png\" alt=\"primeira lei - exemplo - ciclo de brayton\" width=\"300\" height=\"244\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/first-law-example-brayton-cycle-300x244.png\" \/><\/a><figcaption id=\"caption-attachment-16843\" class=\"wp-caption-text\"><span>O ciclo ideal de Brayton consiste em quatro processos termodin\u00e2micos.\u00a0Dois processos isentr\u00f3picos e dois processos isob\u00e1ricos.<\/span><\/figcaption><\/figure>\n<p><strong><span>compress\u00e3o isentr\u00f3pica<\/span><\/strong><span>\u00a0&#8211; o ar ambiente \u00e9 aspirado para o compressor, onde \u00e9 pressurizado (1 \u2192 2).\u00a0O trabalho necess\u00e1rio para o compressor \u00e9 dado por\u00a0<\/span><strong><span>W\u00a0<\/span><\/strong><strong><sub><span>C<\/span><\/sub><\/strong><strong><span>\u00a0= H\u00a0<\/span><\/strong><strong><sub><span>2<\/span><\/sub><\/strong><strong><span>\u00a0&#8211; H\u00a0<\/span><\/strong><strong><sub><span>1<\/span><\/sub><\/strong><strong><span>\u00a0.<\/span><\/strong><\/li>\n<li><strong><span>adi\u00e7\u00e3o de calor isob\u00e1rico<\/span><\/strong><span>\u00a0&#8211; o ar comprimido passa por uma c\u00e2mara de combust\u00e3o, onde o combust\u00edvel \u00e9 queimado e o ar ou outro meio \u00e9 aquecido (2 \u2192 3).\u00a0\u00c9 um processo de press\u00e3o constante, j\u00e1 que a c\u00e2mara est\u00e1 aberta para entrar e sair.\u00a0O calor l\u00edquido adicionado \u00e9 dado por\u00a0<\/span><strong><span>Q\u00a0<\/span><\/strong><strong><sub><span>add<\/span><\/sub><\/strong><strong><span>\u00a0= H\u00a0<\/span><\/strong><strong><sub><span>3<\/span><\/sub><\/strong><strong><span>\u00a0&#8211; H\u00a0<\/span><\/strong><strong><sub><span>2<\/span><\/sub><\/strong><\/li>\n<li><strong><span>expans\u00e3o isentr\u00f3pica<\/span><\/strong><span>\u00a0&#8211; o ar aquecido e pressurizado se expande na turbina, gasta sua energia.\u00a0O trabalho realizado pela turbina \u00e9 dado por\u00a0<\/span><strong><span>W\u00a0<\/span><\/strong><strong><sub><span>T<\/span><\/sub><\/strong><strong><span>\u00a0= H\u00a0<\/span><\/strong><strong><sub><span>4<\/span><\/sub><\/strong><strong><span>\u00a0&#8211; H\u00a0<\/span><\/strong><strong><sub><span>3<\/span><\/sub><\/strong><\/li>\n<li><strong><span>rejei\u00e7\u00e3o de calor isob\u00e1rica<\/span><\/strong><span>\u00a0&#8211; o calor residual deve ser rejeitado para fechar o ciclo.\u00a0O calor l\u00edquido rejeitado \u00e9 dado por\u00a0<\/span><strong><span>Q\u00a0<\/span><\/strong><strong><sub><span>re<\/span><\/sub><\/strong><strong><span>\u00a0= H\u00a0<\/span><\/strong><strong><sub><span>4<\/span><\/sub><\/strong><strong><span>\u00a0&#8211; H\u00a0<\/span><\/strong><strong><sub><span>1<\/span><\/sub><\/strong><\/li>\n<\/ol>\n<p><span>Como pode ser visto, podemos descrever e calcular (por exemplo, efici\u00eancia termodin\u00e2mica) esses ciclos (da mesma forma para o\u00a0<\/span><strong><span>ciclo de Rankine<\/span><\/strong><span>\u00a0) usando\u00a0<\/span><a title=\"O que \u00e9 entalpia\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/what-is-energy-physics\/what-is-enthalpy\/\"><span>entalpias<\/span><\/a><span>\u00a0.<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<p>&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;.<\/p>\n<p>Este artigo \u00e9 baseado na tradu\u00e7\u00e3o autom\u00e1tica do artigo original em ingl\u00eas. Para mais informa\u00e7\u00f5es, consulte o artigo em ingl\u00eas. Voc\u00ea pode nos ajudar. Se voc\u00ea deseja corrigir a tradu\u00e7\u00e3o, envie-a para: translations@nuclear-power.com ou preencha o formul\u00e1rio de tradu\u00e7\u00e3o on-line. Agradecemos sua ajuda, atualizaremos a tradu\u00e7\u00e3o o mais r\u00e1pido poss\u00edvel. Obrigado.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Na termodin\u00e2mica, o trabalho realizado por um sistema \u00e9 a energia transferida pelo sistema para os arredores.\u00a0O trabalho \u00e9 uma forma de energia, mas \u00e9 energia em tr\u00e2nsito.\u00a0Engenharia T\u00e9rmica Trabalho em Termodin\u00e2mica Na termodin\u00e2mica, o\u00a0trabalho\u00a0realizado por um sistema \u00e9 a energia transferida pelo sistema para os arredores.\u00a0Energia cin\u00e9tica, energia potencial e energia interna s\u00e3o formas &#8230; <a title=\"O que \u00e9 trabalho em termodin\u00e2mica &#8211; defini\u00e7\u00e3o\" class=\"read-more\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-trabalho-em-termodinamica-definicao\/\" aria-label=\"More on O que \u00e9 trabalho em termodin\u00e2mica &#8211; defini\u00e7\u00e3o\">Ler mais<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[14],"tags":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v15.4 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>O que \u00e9 trabalho em termodin\u00e2mica - defini\u00e7\u00e3o<\/title>\n<meta name=\"description\" content=\"Na termodin\u00e2mica, o trabalho realizado por um sistema \u00e9 a energia transferida pelo sistema para os arredores. 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